This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Successful cardiac transplantation depends on the ability to adequately protect the donor heart during procurement and transport. To date this has been accomplished by infusing a cold preservation solution into the heart and storing the heart in an ice chest (static preservation). This method has limitations and has led to the development of techniques that provide a continuous flow of oxygenated solution to the donor heart during transport (machine perfusion preservation). This new strategy may allow ongoing oxidative metabolism in the myocardium which can support essential cellular processes. However, existing preservation solutions are designed for static preservation and are not well suited to take advantage of the conditions provided by machine perfusion. This project will examine myocardial metabolism during and after machine perfusion preservation to identify substrate conditions in the preservation solution that maximize oxidative metabolism. Additional experiments will test the concept that increased metabolism during storage leads to superior functional results after transplantation. The specific aims of this research project are: 1) To test the hypothesis that different exogenous substrates affect the degree of myocardial oxidative metabolism in a small animal model of machine perfusion preservation for heart transplantation. 2) To determine the optimal substrate composition and substrate concentration in a perfusion solution to maximize oxidative metabolism during machine perfusion preservation. 3) To test the hypothesis that altering perfusion solution substrate composition leads to similar effects on oxidative metabolism in a large animal (canine) model where flow rates and heart size are different. 4) To test the effect of increased rates of oxidative metabolism of exogenous substrates during machine perfusion preservation on post-transplant ventricular function and cellular damage from necrosis and apoptosis in a large animal model. Information from these studies may enable us to develop improved perfusion solutions for use with machine perfusion preservation, leading to superior results in cardiac transplantation.